Carbon nanostructures (CNSs) refer to nano-sized carbon structures having various shapes such as nanotube, fullerene, nanocone, nanohorn, nanorod, and can be used in diverse technical fields due to their various excellent properties.
Among them, particularly, carbon nanotube (CNT) is a material wherein carbon atoms are arranged in a hexagonal pattern in a tube shape, and has diameter of about 1 to 100 nm. The carbon nanotube shows non-conductive, conductive or semiconductive characteristics according to unique chirality; about 100 times higher tensile strength than steel due to carbon atoms connected by strong covalent bonds; excellent flexibility and elasticity; and chemical stability.
The carbon nanotube is classified into: a single-walled carbon nanotube (SWCNT) consisting of one sheet and having diameter of about 1 nm; double-walled carbon nanotube (DWCNT) consisting of two sheets and having diameter of about 1.4 to 3 nm; and multi-walled carbon nanotube (MWCNT) consisting of three or more sheet and having diameter of about 5 to 100 nm.
Due to its characteristics such as chemical stability, and excellent flexibility and elasticity, studies on its manufacturization and application of the carbon nanotube are in progress in various fields, for example, aerospace, fuel cell, composite material, biotechnology, medicine, electronics, and semiconductor. However, primary structure of the carbon nanotube has limit on directly controlling its diameter or length to the actual standard enough for industrial application. Accordingly, the carbon nanotube has many limits on industrial adaptation or application despite of its excellent properties.
In order to more diversify the roles of the carbon nanostructure such as the carbon nanotube as a structure reinforcement member and a chemical functional body, a method collectively forming a primary structure of the carbon nanostructures on a flat substrate followed by physically growing thereof through a separate spinning process has been used [Zhang, X.; Li, Q.; Tu, Y.; Li, Y.; Coulter, J. Y.; Zheng, L.; Zhao, Y.; Jia, Q.; Peterson, D. E.; Zhu, Y. Small, 2007, 3, 244]. However, this previous method needs a secondary spinning process after flat-type growth, thereby its productivity is very low. The carbon nanotube yarn produced by this process has multi-layered structure grown as a flat-type as shown in FIG. 1 [Adv. Mater. Vol. 22, 2010, pages 692-696(2009, Nov. 24)]
In addition, methods for manufacturing carbon nanotube bundles having various structures and sizes have been reported, and the structures manufactured by the methods are shown in FIG. 2 [(a) Jia, Y.; He, L.; Kong, L.; Liu, J.; Guo, Z.; Meng, F.; Luo, T.; Li, M.; Liu, J. Carbon, 2009, 47, 1652; (b) Zhang, X.; Cao, A.; Li, Y.; Xu, C.; Liang, J.; Wu, D.; Wei, B. Chem. Phys. Lett., 2002, 351, 183; (c) Kathyayini, H.; Willems, I.; Fonseca, A.; Nagy, J. B.; Nagaraju, N. Cat. Commun., 2006, 7, 140; (d) Li, Y.; Zhang, X. B.; Tao, X. Y.; Xu, J. M.; Huang, W. Z.; Luo, J. H.; Luo, Z. Q.; Li, T.; Liu, F.; Bao, Y.; Geise, H. J. Carbon, 2005, 43, 295]. The structures in FIG. 2 are different in individual shape and size, but are similar in that they are not a hollow type but a closely packed type.
In nano-chemistry, the hollow type structure has many advantages. Accordingly, if the hollow type structure can be formed by using the carbon nanostructure having excellent chemical stability, elasticity and flexibility, its utilization will more and more increase.